Pre-press color-proofing is a procedure that is used by the printing industry for creating representative images of printed material without the high cost and time that is required to actually produce printing plates and set up a high-speed, high volume, printing press to produce an example of an intended image. These intended images may require several corrections and be reproduced several times to satisfy customer requirements. Pre-press color-proofing saves time and money getting to an acceptable finished product.
Once an intended image meets the customers requirements, films required for exposing printing plates are generated. These films are currently generated on a separate apparatus such as an imagesetter. The imagesetter recording film is used to prepare printing plates which are used to print finished copies in high volume.
An example of a commercially available image processing apparatus is shown in commonly assigned U.S. Pat. No. 5,268,708. This image processing apparatus is arranged to form an intended image on a sheet of thermal print media in which dye from a sheet of dye donor material is transferred to the thermal print media by applying thermal energy to the dye donor material. The image processing apparatus is comprised generally of a material supply assembly, a lathe bed scanning subsystem (which includes a lathe bed scanning frame, translation drive, translation stage member, printhead, and vacuum imaging drum), and thermal print media and dye donor material exit transports.
The operation of the image processing apparatus comprises metering a length of the thermal print media, in roll form, from the material assembly or carousel. The thermal print media is measured and cut into sheets of required length, transported to the vacuum imaging drum, registered, wrapped around, and secured to the vacuum imaging drum. A length of dye donor material is metered from a roll on the material supply assembly, measured, and cut into sheets of required length. The dye donor material is transported to and wrapped around the vacuum imaging drum, superposed and in registration with the thermal print media.
The thermal print media and the dye donor material are held on the spinning vacuum imaging drum by a vacuum and applied through holes in the surface of the drum while it is rotated past the printhead. The translation drive moves the printhead and translation stage member axially along the vacuum imaging drum in coordinated motion with the rotating vacuum imaging drum to produce the intended image on the thermal print media.
After the intended image has been written on the thermal print media, the dye donor material is removed from the vacuum imaging drum without disturbing the thermal print media beneath it. The dye donor material is transported out of the image processing apparatus by the dye donor material exit transport. Additional sheets of dye donor material, each a different color, are sequentially superposed with the thermal print media on the vacuum imaging drum and imaged onto the thermal print media as described above, until the intended image is completed. The completed image on the thermal print media is unloaded from the vacuum imaging drum and transported to an external holding tray on the image processing apparatus by the exit transport.
The material supply assembly comprises a carousel mounted for rotation about its horizontal axis on bearings at the upper ends of vertical supports. The carousel comprises a vertical circular plate having six material support spindles. These support spindles are arranged to carry one roll of thermal print media, and four rolls of dye donor material to provide the four primary colors used in the writing process to form the intended image and an additional roll, either a spare or a specialty color dye donor material. Each spindle has a feeder assembly to withdraw the thermal print media or dye donor material from the spindles to be cut into a sheet form. The carousel is rotated about its axis into the desired position, so that the thermal print media or dye donor material can be withdrawn, measured, and cut into sheet form of the required length, and then transported to the vacuum imaging drum.
The scanning subsystem generates a once per revolution timing signal to the data path electronics and linear control system as a clock signal while the translation drive traverses the printhead axially along the vacuum imaging drum in a coordinated motion with the vacuum imaging drum rotating past the printhead. This allows precise control of placement of each pixel to produce the intended image on the thermal print media.
The printhead includes a plurality of lasers diodes, individually modulated to supply energy to the thermal print media in accordance with an information signal. A plurality of optical fibers coupled to the laser diodes at one end, and the end to a fiber optic array within the printhead. The printhead is movable relative to the longitudinal axis of the vacuum imaging drum. The dye is transferred to the thermal print media as the radiation, transferred from the laser diodes by the optical fibers to the printhead and thus to the dye donor material, is converted to thermal energy in the dye donor material.
The vacuum imaging drum is cylindrical in shape and includes a hollow interior portion. A plurality of holes extends through a surface of the drum applying a vacuum from the interior of the vacuum imaging drum, which maintains the position of the thermal print media and dye donor material as the vacuum imaging drum rotates.
The ends of the vacuum imaging drum are enclosed by cylindrical plates, each containing a centrally disposed spindle. The spindles extend through support bearings and are attached to the lathe bed scanning frame. The drive end spindle extends through the support bearing and is stepped down to receive a DC drive motor armature. The opposite spindle is provided with a central vacuum opening in alignment with a vacuum fitting with an external flange that is rigidly mounted to the lathe bed scanning frame. The vacuum fitting has an extension which is closely spaced with the vacuum spindle forming a small clearance, which configuration provides a slight vacuum leak between the outer diameter of the vacuum fitting and the inner diameter of the opening of the vacuum spindle. This assures that no contact exists between the vacuum fitting and the vacuum imaging drum which might impart uneven movement to the vacuum imaging drum during its rotation.
The opposite end of the vacuum fitting is connected to a high-volume vacuum blower which produces a vacuum of 50-60 inches of water (93.5-112.2 mm of mercury) at an air flow volume of 60-70 cfm (28.368-33.096 liters/sec). The vacuum required varies during the loading, scanning, and unloading of the thermal print media and the dye donor materials. With no media loaded on the vacuum imaging drum, the internal vacuum level of the vacuum imaging drum is approximately 10-15 inches of water (18.7-28.05 mm of mercury). With the thermal print media loaded on the vacuum imaging drum, the internal vacuum level of the vacuum imaging drum is approximately 20-25 inches of water (37.4-46.75 mm of mercury). This level is required when a dye donor is material is removed, otherwise the thermal print media may move and color-to-color registration will not be maintained as sheets of dye donor material are changed. With both the thermal print media and dye donor material completely loaded on the vacuum imaging drum, the internal vacuum level of the vacuum imaging drum is approximately 50-60 inches of water (93.5-112.2 mm of mercury).
The outer surface of the vacuum imaging drum is provided with an axially extending flat, which extends approximately 8.degree. around the vacuum imaging drum circumference. The vacuum imaging drum is also provided with a circumferential recess which extends circumferentially from one side of the axially extending flat circumferentially around the vacuum imaging drum to the other side of the axially extending flat, and from approximately one inch (25.4 mm) from one end to approximately one inch (25.4 mm) from the other end of the vacuum imaging drum. The thermal print media, when mounted on the vacuum imaging drum, is seated in the circumferential recess. The circumferential recess has a depth substantially equal to the thermal print media thickness, approximately 0.004 inches (0.102 mm).
The purpose of the circumferential recess on the vacuum imaging drum surface is to eliminate any creases in the dye donor material as it is drawn down over the thermal print media during loading. This assures that no folds or creases will be generated in the dye donor material which could extend into the image area which would adversely affect the intended image. The circumferential recess also substantially eliminates the entrapment of air along the edge of the thermal print media where it is difficult for the vacuum holes in the vacuum imaging drum surface to assure the removal of the entrapped air. Any residual air between the thermal print media and the dye donor material can also adversely affect the intended image.
The purpose of the vacuum imaging drum axially extending flat assures that the leading and trailing ends of the dye donor material are protected from the effects of air turbulence during high speed rotation of the vacuum imaging drum during imaging process. Without the axially extending flat, the air turbulence would tend to lift the leading or trailing edge of the dye donor material. The vacuum imaging drum axially extending flat also ensures that the leading and trailing ends of the dye donor material are recessed from the vacuum imaging drum periphery. This reduces the chance of the dye donor material contacting other parts of the image processing apparatus, such as the printhead, which may cause a jam, loss of the intended image, or catastrophic damage to the image processing apparatus.
The task of loading and unloading the dye donor material on the vacuum imaging drum requires precise positioning of thermal print media and the dye donor materials. The lead edge positioning of dye donor material must be accurately controlled during this process. The existing image processing apparatus design employs a multi-chambered vacuum imaging drum for such lead edge control. One chamber applies vacuum to hold the leading edge of the dye donor material. Another chamber, separately valved, controls vacuum which holds the trailing edge of the thermal print media to the vacuum imaging drum. With this arrangement, loading a sheet of thermal print media and dye donor material requires that the image processing apparatus feed the lead edge of the thermal print media and dye donor material into position just past the vacuum ports controlled by the respective valved chamber. As vacuum is applied, the leading edge of the a dye donor material is pulled against the vacuum imaging drum surface.
Unloading the dye donor material, or the thermal print media, requires removal of vacuum from these same chambers so that an edge of the thermal print media, or the dye donor material, is freed and projects out from the surface of the vacuum imaging drum. The image processing apparatus then positions an articulating skive into the path of the free edge to lift the edge and to feed the dye donor material to a waste bin or the thermal print media to an output tray.
The sheet material exit transports consist of a dye donor material waste exit and the imaged thermal print media sheet material exit. The dye donor material exit transport comprises a waste dye donor material stripper blade disposed adjacent the upper surface of the vacuum imaging drum. In the unload position, the stripper blade is in contact with the waste dye donor material on the vacuum imaging drum surface. When not in operation, the stripper blade is moved up and away from the surface of the vacuum imaging drum. A driven waste dye donor material transport belt is arranged horizontally to carry the waste dye donor material which is removed by the stripper blade from the surface of the vacuum imaging drum to an exit formed in the exterior of the image processing apparatus. A waste bin for the waste dye donor materials is separate from the image processing apparatus. The imaged thermal print media sheet material exit transport comprises a movable thermal print media sheet material stripper blade that is disposed adjacent to the upper surface of the vacuum imaging drum. In the unload position, the stepper blade is in contact with the imaged thermal print media on the vacuum imaging drum surface. In the inoperative position, it is moved up and away from the surface of the vacuum imaging drum. A driven thermal print media sheet material transport belt is arranged horizontally to carry the imaged thermal print media removed by the stripper blade from the surface of the vacuum imaging drum. It then delivers the imaged thermal print media with the intended image formed thereon to an exit tray in the exterior of the image processing apparatus.
Although the presently known and utilized color-proofing apparatus is satisfactory, a separate apparatus is needed to expose the imagesetter recording film. Use of a separate machine to produce imagesetter recording film for making printing plates is not efficient since two separate machines must be purchased and maintained. Thus, there is a need to expose imagesetter recording film on the same apparatus that generates contract proofs.